Abstract

The fractions and dimension of bars, rings and lenses are studied in the
near-infrared (IR) S0 galaxy survey, which is a sample of ˜200
early-type disc galaxies, mainly S0s. We find evidence that multiple
lenses in some barred S0s are related to bar resonances in a similar
manner as the inner and outer rings, for which the outer/inner length
ratio is ˜2. Inner lenses in the non-barred galaxies normalized to
galaxy diameter are clearly smaller than those in the barred systems.
Interestingly, these small lenses in the non-barred galaxies have
similar sizes as barlenses (lens-like structures embedded in a bar), and
therefore might actually be barlenses in former barred galaxies, in
which the outer, more elongated bar component has been destroyed. We
also find that fully developed inner lenses are on average a factor of
1.3 larger than bars, whereas inner rings have similar sizes as bars.
The fraction of inner lenses is found to be constant in all family
classes (A, AB, B). Nuclear bars appear most frequently among the weakly
barred (AB) galaxies, which are consistent with the theoretical models
by Maciejewski & Athanassoula. Similar-sized bars as the nuclear
bars were detected in seven `non-barred' S0s. Galaxy luminosity does not
uniquely define the sizes of bars or bar-related structures, neither is
there any upper limit in galaxy luminosity for bar formation. Although
all the family classes cover the same range of galaxy luminosity, the
non-barred (A) galaxies are on average 0.6 mag brighter than the
strongly barred (B) systems. Overall, our results are consistent with
the idea that bars play an important role in the formation of the
structure components of galaxies. The fact that multiple lenses are
common in S0s, and that at least the inner lenses can have very old
stellar populations, implies that the last destructive merger or major
gas accretion event, must have taken place at a fairly high redshift.